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Peroxisomes ...

Are membrane bounded organelles that appear in most eucariotic cells. They have often a crystalline structure within the amorphous gray matrix (Fig. 1). There are animals in which other kind of inclusions may exist or even in which there are no inclusions at all (Figs. 2, 3). Peroxisomes are self replicating! In mammals and other vertebrates they are particularly large and abundant in hepatocytes and cells of the tubular portions of the nephrons (namely in the epithelial cells of the proximal tubules). Peroxisomes were discovered only in 1954, and their function was virtually unknown for over a decade. Today, they are known to be essential in many vital pathways such as the:

metabolism of free oxygen radicals;
synthesis of cholesterol and ether lipids;
bile acid formation;
catabolism of long chain fatty acids;
catabolism of purines, prostaglandins, leucotriens;
alcohol detoxification in liver;
metabolism of estradiol (more recently proved, and our currently research topic).

Some interesting facts about peroxisomes are:

human congenital diseases are associated with the absence of peroxisomes and/or with the dysfunction of their enzymes;
many chemicals (drugs, industrial pollutants) induce a marked proliferation of peroxisomes;
prolonged treatment with most proliferators induce malignant hepatic tumours;
estradiol seems to have a depressive effect on peroxisomes (at least in fish hepatocytes).

Fig. 1 - Transmission electron microscopy (TEM) micrograph of a peroxisome from the marine snail Gibulla umbilicalis.

Fig. 2 - TEM micrograph of a peroxisome of an hepatocyte from brown trout, Salmo trutta. There are no inclusions!

Fig. 3 - Peroxisome from the marine mollusc Lepidochitona cinerea, having crystalline and non-crystalline inclusions.

(All pictures were taken by Prof. Alexandre Lobo-da-Cunha, at our electron microscopy unit) [TOP]

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